How to make a walking animation for a character in the BGE on a uneven or steep floor?
Ok,

you can change the angle of the step, easy enough with a ray, and parenting the animation
handles to a empty that animate the feet, just use track to another empty on the empty the feet animation handles are parented to, and place the empty via a ray. (so the player will walk up and down hills and change stride angle)

The hardest way (and best way) is this

http://www.youtube.com/watch?v=ZtzQAluEgts

This is a walking ragdoll, that uses the step offset angle code, along with the fact that it really walks.....

http://blenderartists.org/forum/showthread.php?353549-Non-PID-Ragdoll-based-on-Jackii-s-work-made-for-quot-Wrectified-quot

here is the 'base' of that rig.